A SIMPLE APPROACH TO CREATING SIMPACTED DATA TO ESTABLISH THE POWER OF RCA ASSESSMENT METHODS.

The statistical power of bioassessment methods is rarely discussed. Typically the only statistical tests applied are those addressing the null hypothesis that a site is equivalent to reference or control and the alpha level used sets the Type 1 error level. However, Type 2 error is rarely considered as there is no a priori method for knowing if an exposed site is disturbed. We suggest that the method for resolving this issue is to create artificially disturbed sites by modifying data from reference sites. This method uses a stressor such as organic discharge and then using known tolerance values adjusts the counts at reference site(s) to create a theoretically disturbed (SIMPACT) community with a known level of disturbance. The various assessment methods can then be used to determine if the method has the power to detect the simulated impact. Two questions arise from this, first is this a reasonable method for creating simulated communities, and second what levels of simulated disturbance should we be able to detect?